automatic rate adaptation

Tony Espy espy
Fri Jul 29 12:13:26 PDT 2005

Eduard GV wrote:
> Thanks Jouni,
> but could you explain the details of the mechanism? Or is there any
> reference you could point me to?

The details can be found in the Prism Driver Programmer's Manual.  you 
need to contact Connexant to get a copy ( unless you can find one on the 
net ).

A short summary of the mechanism in managed mode:

1. Rate fallback is triggered by transmit retries.  The default behavior 
is to fallback to the next lowest rate starting at the 3rd TX retry and 
then again for each subsequent retry.  So the first fallback is from 
11Mbps to 5.5Mbps, then to 2, then to 1.

2. The trigger of the rateFallbackTimer ( hard-coded to 10 seconds ) or 
a number of successful transmissions ( I don't know how many this is ) 
controls upgrade back to the highest rate.  The timer is initiated by 
occurence of the first rate fallback.

Tony Espy
Pepper Computer, Inc.

> I mean, how is it handled? For example, does it count lost ACKs (after
> S consecutive ACKed frames the rate is increased and after E
> consecutive lost ACKs rate is lowered), does it use any timer, etc.?
> Thank you again.
> On 7/29/05, Jouni Malinen wrote:
>>On Thu, Jul 28, 2005 at 04:45:30PM +0200, Eduard GV wrote:
>>>I would like to know if prism cards implement any kind of rate
>>>adaptation algorithm (change modulation depending on channel
>>>If yes, could you explain the mechanism? is it carried out by the
>>>firmware or by hostap driver?
>>Yes, station firmware implements a rate control algorithm. In addition,
>>the driver can override the TX rate selection on packet-by-packet basis.
>>As an example, Host AP driver uses its own algorithm for the Master/Host
>>AP mode since firmware implementation is mainly for managed modes.
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